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PHP Functions

A function is a type of procedure or routine.
  • A function is a group of statements.
  • A function is not executed until it is called
  • A function can be called as many times as you need, in a script.

PHP Built-In Functions

PHP has thousands of built-in functions. Each of those functions is focused to perform a specific task. We have already discussed four of them.

  • echo() - to output a string
  • print() - to output a string
  • define() - to define a constant
  • var_dump() - to dump data of a variable

You will learn about these functions step-by-step in this tutorial.

PHP User-Defined Functions

The function declaration starts with function keyword. Then, the function name and arguments.

function functionName(arg1, arg2, ....) { code to be executed }

PHP Naming User-Defined Functions

Function naming is almost same as variable naming except adding a $ sign into the beginning. Functions does not have $ sign.

  • A function name should start with a letter or underscore.
  • A function name cannot start with a number.
  • Letters, numbers and underscores can be used after the first letter in a function.
  • A function name is case-insensitive (Both boom() and Boom() refers the same function.)
  • Tip: Always name functions with a name that describes the usage of the function.

PHP Declaring User-Defined Functions

Let's create our first function.

  • First, we declare the function greet() using function syntax.
  • The block of code inside the curly braces ({}) is the function code. This code is executed when we call the function.
  • Then, we call our function using its name and parentheses: greet();

Note: We always use parentheses to call a function.

PHP User-Defined Function Example


<?php
function greet() {
	$hour = date('G'); // get the hour in 24-hour format
	if ($hour < 12) {
		echo 'Good Morning';
	} else if ($hour < 17) {
		echo 'Good Afternoon';
	} else {
		echo 'Good Night';
	}
}

greet(); // calling the function

Run Example ››

PHP Function Arguments

We can get different results from a function using arguments.

Function arguments are the values passed into a function. An argument is a variable inside function.

  • Arguments are defined inside the parentheses which are immediately after the function name.
  • A function can have any number of arguments, separating them with a comma.
  • A argument name has the same rules as a variable.

Let's see an example.

  • First, we declare a function named myName with one argument, $name.
  • Then, we call the function several times with different values.
  • Note the value inside the parentheses of the function call. That value is assigned to $name when the function executes.

PHP Function Arguments Example


<?php
function myName($name) {
	echo 'My name is ' . $name; 
	echo '<br>'; // line break
} 
myName('Joe'); 
myName('Adam');
myName('David');

Run Example ››

Functions can have multiple arguments.

PHP Function Multiple Arguments Example


<?php
function myDetails($name, $age, $country) {
	echo "
		My name is $name <br>
		My age is $age <br>
		My country is $country <br><br>
	";
}
myDetails('Joe', 22, 'USA');
myDetails('Adam', 25, 'United Kingdom');
myDetails('David', 30, 'France');

Run Example ››

PHP Function Arguments - Passing By Reference

By default, arguments are passed into functions by value. See the following example to understand it.

PHP Passing Arguments By Value Example


<?php
function changeName($name) {
	$name .= ' Developer';
	echo 'Inside the function: ' . $name . '<br>'; // outputs "Hyvor Developer"
}
$rootName = 'Hyvor';
changeName($rootName);
echo 'Outside the function: ' . $rootName; // it is stil 'Hyvor'


Run Example ››

In the above example,

  • $rootName variable is set to "Hyvor".
  • Then, it is passed into changeName() function as the $name argument.
  • Inside the function, "Hyvor" is changed to "Hyvor Developer".
  • But, after executing the function the global variable $rootName still holds the value "Hyvor".

You can change the value of an argument by passing them by reference. Just prepend an & sign to the argument name in the function definition.

PHP Passing Arguments By Reference Example


<?php
function changeName(&$name) {
	$name .= ' Developer';
	echo 'Inside the function: ' . $name . '<br>'; // outputs "Hyvor Developer"
}
$rootName = 'Hyvor';
changeName($rootName);
echo 'Outside the function: ' . $rootName; // it is stil 'Hyvor'


Run Example ››

PHP Function Arguments - Default Values

To specify a default value for an argument, just assign that with the basic assignment operator (=) in the function definition. If the argument is not provided when calling the function, this default value is used.

PHP Functions - Default Values for Arguments Example


<?php
function printNumber($number = 10) {
	echo "The number is: $number <br>";
}

printNumber(2);
printNumber(25);
printNumber(); // will print 10, the default value
printNumber(500);

Run Example ››

PHP Functions - Returning

There are two uses of return statements.

  • To return a value from a function.
  • To stop the execution of a function when certain condition is true.

PHP Functions - Returning Values

PHP Functions - Returning Values Example


<?php
function sum($num1, $num2) {
	return $num1 + $num2;
}

echo '5 + 5 = ' . sum(5,5) . '<br>';
echo '4 + 3 = ' . sum(4,3) . '<br>';
echo '8 + 1 = ' . sum(8,1) . '<br>';

Run Example ››
Since PHP 7, you can define the data type of the returning value.

PHP Functions - Returning Values with a Specific Data Type


<?php
function sum($num1, $num2) : float {
	return $num1 + $num2;
}
var_dump(sum(5, 2)); // float value is returned

Run Example ››

PHP Variable Functions

If a variable which contains a string has parentheses appended to it, PHP checks for a function with the same name, and will execute it. This concept is called variable functions.

PHP Variable Functions Example


<?php
function printSentence() {
	echo "My name is Hyvor Developer";
}
$functionName = 'printSentence';
$functionName(); // called printSentence function

Run Example ››
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